Field of the Invention
The present invention relates to a material composed of a silica shell including an aqueous phase comprising at least one droplet of crystallizable oil in the solid state, to its process of preparation, to its use for the thermostimulated delivery of active substances and to the compositions including such a material.
Description of Related Art
It may be of use to encapsulate molecules of interest, such as medicaments, dyes, pigments, reactants, fragrances, pesticides, and the like, in order to protect them from external attacks, in particular from oxidation, in order to convey them to a site of administration where they can be delivered or else in order to store them before use under conditions where they will be released from their capsule under the influence of an external stimulus. One of the first applications of microencapsulation was the development of a carbonless copy paper commercialized at the end of the 1960s, in which microcapsules imprisoning an ink were present on the back of a paper sheet so as to release the ink by rupture of the capsules under the pressure exerted by the tip of a pen during writing. At the present time, encapsulation is growing in various industrial sectors, such as pharmaceutical, cosmetics, food, textile and agricultural industries. Capsules and microcapsules are becoming increasingly sophisticated, in particular in the pharmaceutical field, where they make it possible to bring about the controlled and/or targeted delivery of active principles.
Various types and morphologies of capsules and microcapsules have already been provided, such as, for example, protein capsules, cyclodextrins, liposomes, concentrated lamellar vesicles, double emulsions, colloidosomes, microcapsules comprising silica shells, nanocapsules of silica and of heat-sensitive polymers, such as poly(N-isopropylacrylamide) (PNIPAM), heat-sensitive hydrogel microspheres, PNIPAM-Polylactide microspheres, and the like. Numerous methods which make it possible to prepare these various types of capsules and microcapsules have also been developed and perfected in recent years, such as, for example and non-exhaustively, the precipitation of polymers by phase separation, layer-by-layer electrolyte deposition, polymerization by interfacial polycondensation, and the like.
The disadvantage of the techniques already known is that the release of the molecules of interest from the capsules and microcapsules provided in the prior art is generally slow and gradual, that is to say prolonged over time.
Provision was then made to overcome this problem by providing materials composed of a silica shell including a wax core comprising one or more substances of interest, these materials being prepared by mineralization of a Pickering emulsion, that is to say of an emulsion of oil-in-water type in which the dispersion of the oil droplets in the water is stabilized by colloidal nanoparticles adsorbed at the water/oil interface (see, for example, Patent Application FR-A-2 948 581). By using a crystallizable oil to prepare these materials, that is to say an oil having a fairly low melting point (TM) (for example, 37° C.), it is possible to prepare materials in which the encapsulated phase is solid under the storage conditions (for example, at ambient temperature) but becomes liquid under the conditions of use of the material (for example, at a temperature greater than 37° C. in the case of an ingestible or injectable medicament), thus bringing about the rupture of the capsule by melting and thermal expansion of the encapsulated phase and the concomitant and rapid release of the active substance or substances present in the encapsulated phase. These materials make it possible to encapsulate both lipophilic substances of interest (in the dissolved form) and hydrophilic substances of interest (in the dispersed form). However, when the encapsulated phase of these materials includes several substances of different chemical nature, these are in contact with one another, which does not make it possible, within one and the same material, to encapsulate substances which may exhibit a chemical and/or physical incompatibility. Furthermore, these materials do not make it possible to simultaneously comprise hydrophilic and lipophilic substances both in the dissolved form since only the lipophilic substances can be present in the dissolved form in the fatty phase encapsulated by the silica shell, whereas the hydrophilic substances are in the dispersed form therein.
There thus currently does not exist a compartmentalized system which makes it possible to encapsulate in the dissolved form, within one and the same material, at least two substances of interest which may furthermore possibly be incompatible with one another, said substances being lipophilic or hydrophilic, and which allows rapid and complete release of these substances of interest under the effect of an external stimulus under mild conditions.